We are investigating the mechanism of action of neurotrasmitters, using the glutathione feeding response of Hydra as a model. Many analogs of glutathione (activator) and glutamic acid (inhibitor) have been synthesized and are being tested for their activator and/or inhibitor activity in a quantitative bioassay using intact Hydra. A binding assay with radioactive activators is being developed and cyclic nucleotide levels are being examined in the hope that measurement of these levels may also provide an appropriate assay. Special emphasis is being placed on developing a series of affinity labels and several different affinity columns in order to aid in the isolation and purification of the glutathione receptor.